"Paul was a very erudite guy and very learned. He was a world traveler until he became ill," said Andrew S. Blumberg, a member for many years of the Baltimore Streetcar Museum, where he is director of public relations. "As a longtime board member of the museum, he was the type of man who helped steer the future of the museum."

The son of Dutch immigrant parents, Paul Willem Wirtz was born in Baltimore and spent his early years in Bolton Hill, before moving with his parents to a home on St. Johns Road in Roland Park. His father was a portrait painter and an illustrator, and his mother was a homemaker.

Mr. Wirtz attended the Park School, where he met and became a lifelong friend of Gwinn F. Owens and his family. Mr. Owens, who later became an editorial writer and op-ed page editor of The Evening Sun, died in 2009.

After graduating from the Park School in 1939, Mr. Wirtz earned a bachelor's degree in 1943 from the Johns Hopkins University. He also earned his architectural license in 1954.

He served in the Navy at the Bainbridge Naval Training Station in Cecil County from 1943 to 1946, when he was discharged.

Mr. Wirtz went to work at Aberdeen Proving Ground, where he rose to become deputy director of facilities engineering, a position he held until retiring in the mid-1980s.

"He was incredibly learned and literate and knew a lot about so many things," said Paul von Hartz Owens, a senior editorial writer for the Orlando Sentinel, whose parents, Gwinn F. and Joan Q. Owens, named him for Mr. Wirtz.

"He knew about music, history and technology and was an early adapter to new gadgets before other people," said Mr. Owens. "He inspired me with his intellectual curiosity and had an enthusiasm for learning that was infectious."

He said that for years, Mr. Wirtz spent every Saturday evening at the Owens family home on Locust Avenue in Ruxton.

"Because he had no family and had not married, we became a very close family with him. He came to our home on Saturday nights for decades. It was something my parents looked forward to and the kids looked forward to it as well," said Mr. Owens.

"One of the other things is that Paul had a wonderful sense of humor. It was very droll and understated and he was a big fan of classic comedy like Bob and Ray and Bob Newhart," he said.

Mr. Wirtz's love affair with streetcars and railroads began in his childhood, when his father was commissioned by United Railways & Electric Co., forerunner of the Baltimore Transit Co., to create a series of advertising illustrations for the streetcar company.

"He got the streetcar bug when he was 5 years old when his father traveled the streetcar system and Paul accompanied him. That's how he got hooked," said Mr. Blumberg.

"I think the Baltimore Streetcar Museum was his biggest thing," said Laura G. Templeton of Ruxton, who is Paul Owens' sister.

"His heart was always at the streetcar museum," said Morris Garten, a partner in Fedder & Garten and Mr. Wirtz's legal representative.

"He joined in 1974 and was our comptroller for many years and on our board. He was quite a guy," said John O'Neill, museum president. "While he was obviously interested in the affairs of the museum, he never operated our streetcars. What engendered his love of them, he explained, dated to the 1920s, when he rode with his father."

"In fiscal matters for the museum, he exercised prudence and good judgment, and saw through to the heart of the matter, asking all of the pertinent questions," said Mr. Blumberg. "His training as an architect was also valuable when discussing the museum's physical plant."

"He was the financial brains of the museum," said Herbert R. Harwood Jr., a retired CSX executive and noted railroad historian and author.

Mr. Wirtz was the author of "Baltimore and Streetcars, 1926," which was published by the Baltimore Streetcar Museum in 1988 and reproduced his father's United Railways illustrations. He also edited and proofed the manuscript of Michael R. Farrell's "The History of Baltimore's Streetcars," published by Greenberg Publishing Co. in 1992.

He contributed the foreword to Mr. Harwood's "Baltimore Streetcars: The Postwar Years," published in 2003 by the Johns Hopkins University Press.

"I thought it would be a good idea for Paul to do it. He was a very positive spirit," said Mr. Harwood. "And because he had so many interests, he was always mentally stimulating to be around. It was always fun to get a phone call from him or go and see him and soak up his knowledge."

"During the first part of the 20th century, the streetcar was the greatest single influence on Baltimore's growth, as it was for most American cities," observed Mr. Wirtz, who credited streetcars with creating the suburbs, because workers no longer had to live near their place of employment.

"Almost two thousand streetcars, operating on more than four hundred miles of lines, brought everyone to within a half-hour or less of the city's center," he wrote. "And for decades, the streetcars were everyone's transportation: bankers and clerks, factory workers and managers, domestics, schoolchildren, letter carriers, firemen, and policemen all rode together."

Mr. Wirtz was a fan of ocean liners and enjoyed traveling aboard steamships.

"He also had been the official photographer for the first Pride of Baltimore and sailed aboard her," said Ms. Templeton.

Mr. Wirtz, who was fluent in Dutch, was also an oenophile and a connoisseur of old Maryland rye, she said.

For the past 17 years, he had lived at the Brightwood retirement community in Lutherville.

Funeral services will be held at 10 a.m. Thursday in the chapel of the Garrison Forest Veterans Cemetery, 11501 Garrison Forest Road, Owings Mills.